Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRMaterial characterization of coatings
How do paint layers on plastic components affect radar waves? This question is fundamental for radar sensors installed in cars behind bumpers or other body parts. Fraunhofer FHR provides answers.
Radar sensors enhance safety in vehicles by measuring the distance to other road users and their speed relative to the vehicle. They emit radar waves that are reflected back to the sensor by vehicles or pedestrians, forming the basis for distance control, lane change assistance, or collision warning systems. In many cases, these sensors are invisibly installed behind the vehicle emblem. For design reasons, the sensors for assistance systems are increasingly integrated behind plastic components such as bumpers or rear and side panels. The challenge is that the painted plastic reflects, dampens, and scatters radar waves. The influence of the millimeter-thick plastic can be reasonably determined, but the effects of the various micrometer-thin paint layers on the radar waves are very difficult to analyze and require precise measurement technology.
Investigation in the E-Band and D-Band
Researchers at Fraunhofer FHR, commissioned by BASF Coatings GmbH, have developed a system that allows for the exact determination of the dielectric material parameters of the various paint layers and their influence on radar waves. "Knowing the paint parameters allows us to design, for example, the thickness of the painted plastic component or the paint formulation in such a way that the radar waves are influenced as little as possible," explains Dr.-Ing. Thomas Bertuch, group leader at Fraunhofer FHR. Through market research, the researchers first identified which methods are best suited for measuring the dielectric parameters of a paint layer. The main development challenge was to integrate the purchased components into a mechanical measurement fixture that allows reliable examination of multi-layered painted material samples. "Since any movement of the cables and the measurement setup can cause measurement errors, and the setup needs to be adjusted for daily calibration, this required a very sophisticated arrangement – with three teams from Fraunhofer FHR contributing their expertise," says Bertuch. Another challenge was the development of evaluation software that allows the determination of the material parameters of the layers.
Currently, two systems are already in use at BASF Coatings GmbH in Münster-Hiltrup: one measures the influence of paint layers on radar radiation in the E-band between 60 and 90 gigahertz, and the other in the D-band at 110 to 170 gigahertz.